设arcsinx=a,arcsiny=b
则x=sina,y=sinb
cosa=(1-x^2)^(1/2)
cosb=(1-y^2)^(1/2)
sin(arcsinx+arcsiny)=sin(a+b)
=sinacosb+cosasinb
=x*(1-y^2)^(1/2)+y*(1-x^2)^(1/2)